Alzheimer's disease (AD) is a progressive brain disease with a huge cost to human lives. The impact of the disease is also a growing concern for the governments of developing countries, in particular due to the increasingly high number of elderly citizens at risk. Alzheimer's disease is the most common form of dementia, a common term for memory loss and other cognitive impairments. Generally, dementia include the form of vascular dementia and degenerative dementia including Alzheimer's disease or Alzheimer's dementia. Different Types of dementia are described as amyloidopathy (Alzheimer's dementia), tauopathy (Lewy body disease, Creutzfeld-Jacob disease, Pick's disease), and synucleinopathy (Parkinson's disease).
The biggest risk factor for dementia is age. People over the age of 85 are more likely to experience the condition, although some forms of dementia occur in people under the age of 50. Some individuals are genetically more susceptible to develop certain forms of dementia, such as Alzheimer's and Huntington's diseases. Additionally, several factors can cause temporary or permanent dementia, such as brain injuries (including damage caused by stroke), malnutrition, infections, reaction to medication, poisoning, brain tumor or lesion.
Alzheimer's disease is a chronic progressive neurodegenerative disease and it is the most prevalent type of dementia. Current diagnostic means, including neuroimaging methods, are continuously improving. Nevertheless, it is still a challenge to increase the sensitivity and specificity of a diagnosis of Alzheimer's disease. Two diagnostic areas are especially challenging: first, differentiating early stages of Alzheimer's disease from mild cognitive impairment and normal aging; and second, increasing diagnostic specificity especially when similar clinical symptoms are shared by various types of dementia. To date, the analysis of beta-amyloid(1-42), total tau and phospho-tau-181 from cerebrospinal fluid (CSF) are the best biological markers to diagnose Alzheimer's disease and differentiate it from other forms of dementia with a high reliability and validity. Marksteiner J. et al. (Drugs Today 43(6):423-31, 2007) review the use of CSF biomarkers and of putative blood-related markers. It is suggested that the risk of mild cognitive impairment is influenced by tau protein gene variations and that mild cognitive impairment shares a common genetic background with Alzheimer's disease. This may help elucidating the genetic risk to cognitive decline and designing effective clinical trials. Welge V. et al. (J. Neural. Transm. 116(2):203-12, 2009) reported that for cerebrospinal fluid (CSF) concentrations, the ratio Abeta1-42/Abeta1-38/p-tau powerfully discriminates Alzheimer's disease (AD) from non-Alzheimer dementia patients and fulfils the accuracy requirements for an applicable screening and differential diagnostic AD biomarker.
The Alzheimer's association provides seven stages during the course of disease, namely, 1: no impairment, 2 very mild decline (early stage), 3 mild decline, 4 moderate decline, 5 moderately severe decline, 6 severe decline, and 7 very severe decline.
Early detection of neurodegenerative disorders would enable more effective treatment of patients. Recent studies have demonstrated that disorders like Alzheimer's disease are characterized by a pre-symptomatic phase, likely lasting years, during which neuronal degeneration is occurring but before clinical symptoms appear. This presents both a challenge—how to identify individuals during this preclinical period—and an opportunity. Preventive therapy could be started during the preclinical period before disease symptoms appear. Therefore, a major goal of clinical research is to improve early detection of these diseases by developing tools to move diagnosis backward in the neurodegeneration temporal course. Furthermore, early identification of individuals being at risk of developing Alzheimer's disease is highly desired. It is described in the art that AD prophylaxes and treatment is more effective in patients with early detection of said neurodegenerative disorder as well as of delaying on said end progression of AD.
Aggregated amyloid-beta (Abeta) peptide is implicated in the pathology of Alzheimer's disease. In vitro and in vivo, these aggregates are found in a variety of morphologies, including globular oligomers and linear fibrils, which possess distinct biological activities. Diagnosis and monitoring of sporadic Alzheimer's disease (AD) have long depended on clinical examination of individuals with end-stage disease. However, upcoming anti-AD therapies are optimally initiated when individuals show very mild signs of neurodegeneration. There is a developing consensus for cerebrospinal fluid amyloid-beta (Abeta) as a core biomarker for the mild cognitive impairment stage of AD. Abeta is directly involved in the pathogenesis of AD or tightly correlated with other primary pathogenic factors. It is produced from amyloid precursor protein (APP) by proteolytic processing that depends on the beta-site APP-cleaving enzyme 1 and the gamma-secretase complex, and is degraded by a broad range of proteases.
The 40 and 42 amino-acid residue forms of amyloid-beta (Abeta(1-40) and Abeta(1-42)) in cerebrospinal fluid (CSF) have been proposed as potential biomarkers of Alzheimer's disease (AD). Quantitative analyses of Abeta peptides in CSF have relied almost exclusively on the use of immunosorbent-based assays such as the enzyme-linked immunosorbent assay (ELISA) procedure. However, due to the property of the Abeta peptides to readily self-aggregate or bind to other proteins and glassware, such analyses are extremely challenging. Analyses are further complicated by the potential of the peptides to undergo post-translational modifications and the possibility for cross-reaction in the ELISA assays with endogenous components of the CSF. Recent findings suggest that decreased plasma Abeta(1-42) relative to Abeta(1-40) might increase the risk of AD (Hampel H. et al., Alzheimers Dement. 4(1):38-48, 2008).
Tumor necrosis factor alpha (TNF-alpha) is a multifunctional pro-inflammatory cytokine that belongs to the tumor necrosis factor (TNF) superfamily. This cytokine is mainly secreted by macrophages. It is involved in the regulation of a wide spectrum of biological processes including cell proliferation, differentiation, apoptosis, lipid metabolism, and coagulation. This cytokine has been implicated in a variety of diseases, including autoimmune diseases, insulin resistance, and cancer. Knockout studies in mice also suggested the neuroprotective function of this cytokine.
The concept of inflammation as a major factor in Alzheimer's disease (AD) has heretofore been based on post mortem findings of autodestructive changes associated with the lesions coupled with epidemiological evidence of a protective effect of anti-inflammatory agents. Now there is evidence that the risk of AD is substantially influenced by a total of 10 polymorphisms in the inflammatory agents interleukin 1 alpha, interleukin 1 beta, interleukin 6, tumor necrosis factor alpha, alpha(2)-macroglobulin, and alpha(1)-antichymotrypsin. The polymorphisms are all common ones.
WO 2005/052292 and WO 2006/133423 describe methods and compositions for diagnosis, stratification, and monitoring of AD and other neurological disorders in body fluids. For example, EP 2 211 183 B1 stemming from the above WO application identifies methods for diagnosing and monitoring of AD wherein as a biomarker insulin-like growth factor binding protein 2 (EGFBP-2) is measured. The referenced patent application provides a large number of possible biomarker which should be allegedly suitable for diagnosing neurological disorders including AD. However, a specific set of biomarkers allowing diagnosis and prediction of AD with high accuracy is not disclosed. In addition, Thambisetty, N., et al, biomarkers and medicine, future medicine, London, Volume 4, No. 1, pages 65 to 79, disclose blood based biomarkers of AD: Challenging but feasible. WO 2009/149185 identifies dual variable domain immunoglobulins and uses thereof.
Recent findings have suggested an involvement of brain-derived neurotrophic factor (BDNF) in the pathogenesis of Alzheimer's disease (AD). BDNF is an endogenous protein involved in the maintenance of neuronal function, synaptic plasticity and structural integrity in the adult brain. BDNF serum and cerebrospinal fluid (CSF) concentrations were assessed by a sensitive ELISA in 27 AD patients in comparison to 9 normal pressure hydrocephalus (NPH) patients and 28 age-matched healthy controls. A significant decrease of BDNF serum concentration in AD (18.6 ng/ml) and NPH patients (18.1 ng/ml) was found as compared to healthy controls (21.3 ng/ml; p=0.041/p=0.017). BDNF serum concentrations did not correlate with CSF levels, age or mini mental state examination (MMSE) scores both in AD and NPH patients. The decrease of BDNF serum levels in AD and NPH may reflect a lack of trophic support and thus contribute to progressive degeneration in both diseases.
Chronic inflammation is a characteristic of Alzheimer's disease (AD). An interaction associated with the risk of AD has been reported between polymorphisms in the regulatory regions of the genes for the pro-inflammatory cytokine, interleukin-6 (IL-6), and the anti-inflammatory cytokine, interleukin-10 (IL-10). A dysregulation of both IL-6 and IL-10 in some elderly people, due in part to genetic variations in the two genes, may contribute to the development of AD (Cambarros O. et al., J. Neuroinflammation 23(6):22, 2009).
IL-6 (also named interferon beta 2) is highly elevated in Alzheimer's disease (AD) and has strong correlation to other diseases such as diabetes. IL-6 has also correlations to other neurodegenerative diseases and depression. A role in Alzheimer's disease (AD) is also suspected for the interleukins IL-10, IL-18 and vascular epidermal growth factor (VEGF). Malaguera L. et al. (Neuropathology 26(4):307-12, 2006) determined that the levels of IL-18 was significantly elevated in patients with AD and vascular dementia compared to non-demented, age-matched subjects.
Mateo et al. (Acta Neurol. Scand. 116(1):56-8, 2007) described that vascular endothelial growth factor (VEGF) determines important neurotrophic and neuroprotective actions. Low serum VEGF levels are associated with Alzheimer's disease.
The integrity of neuroprotection is an important component against the development of cognitive disorders and AD. An Alzheimer's disease patient group demonstrated at baseline a severe reduction of insulin-like growth factor-1 (IGF-1) (3.7±1.2 pg/ml), vascular endothelial growth factor (VEGF) (63±18 pg/ml) and TGF-beta 1 (33±10 pg/ml) compared to healthy elderly subjects (IGF-1, 9.5±2.4 pg/ml; VEGF, 105±31 pg/ml; and TGF-beta 1, 68±18 pg/ml). Significant positive correlations between IGF-1 and VEGF concentrations were found both in healthy subjects (r=0.87, p<0.001) and in AD subjects (Luppi C. et al., Arch. Gerontol. Geriatr. 49(Suppl. 1):173-84, 2009).
Elevations in plasma homocysteine are associated with common problems seen with aging, such as cognitive impairment, dementia, depression, osteoporotic fractures, and functional decline. It is known that homocysteine levels are higher in vascular dementia patients than in Alzheimer's disease (AD) patients or controls. Elevated plasma homocysteine concentrations and low serum folate concentrations are independent predictors of the development of dementia and AD. The normal range of plasma homocysteine level is 5-15 μmol/L, for AD patients above 15 μmol/L.
Monocyte chemotactic protein-1 (MCP-1) is highly induced in a variety of diseases that feature monocyte-rich cellular infiltrates such as atherosclerosis, congestive heart failure and rheumatoid arthritis.
The detection of elevated levels of C-reactive protein (CRP) in serum is not specific for any particular disease. It is a useful indicator of inflammatory processes. Plasma CRP is associated with prevalent mild cognitive impairment (MCI) and with non-amnestic MCI in elderly, non-demented persons in a population-based setting. These findings suggest the involvement of inflammation in the pathogenesis of MCI. High plasma CRP level is associated with accelerated cognitive decline and increased risk for dementia in patients with MCI. AD patients had higher CRP levels than vascular dementia patients (4.2±0.6 vs. 1.7±0.2, p<0.001, respectively). Stepwise multiple logistic regression analysis showed that dementia (odds ratio=OR=4.965, 95% confidence interval=CI=1.402-13.23, p=0.004), fibrinogen (OR=1.011, CI=1.007-1.015, p<0.001), and age (OR=1.158, CI=1.063-1.261, p<0.001) are independently correlated with high levels of CRP. The study suggests that inflammation may have a pathogenetic role in AD (Mancinella A. et al., Arch. Gerontol. Geriatr. 49(Suppl 1):185-94, 2009).
There is no current cure for Alzheimer's disease, but there are drug and non-drug based approaches for its treatment. In general the drug treatments are directed at slowing the progression of symptoms. Several biomarkers are well proved to be effective in a large group of patients but success is directly correlated with identifying the disease carriers at its early stages. This justifies the need for timely and accurate forms of diagnosis via molecular means, Ray S. et al., Nat. Med. 13(11):1359-62, 2007. At present, the drug approaches are based mainly on two principles: cholinesterase inhibitors, like donepezil, galantamine, and rivastamine as well as NMDA receptor antagonists like memantine. Further, non-drug based approaches include psychological therapies like psychotherapy, counseling and cognitive behavioral therapy. Other types of mental training are known but also exercises and diet.
To conclude, improved diagnostic screening for early Alzheimer's disease has a number of benefits. Early diagnosis allows people in the early stages of the disease to contribute to the decision making process about medication. Existing medications work best, if they are going to work at all, in the early stages of the disease. Early detection allows early intervention. As medications are developed it could well be that in the future early detection will prevent the irreversible damage to the brain that occurs as Alzheimer's disease progresses. Thus, there is an ongoing need for methods and test systems allowing diagnosing AD at an early stage with high specificity, thus, allowing determination of the treatment regimen in case of diagnosing positively AD. Furthermore, to allow differentiation of AD from other types of dementia, new methods and assays are required. That is, identifying later steps of AD is of help for allowing determination of the treatment regimen.